The present invention relates generally to radar cross-section (RCS) and antenna pattern measurement ranges. More specifically, the present invention relates to a combined projector-low RCS source support/sting pylon for use with low RCS and antenna pattern measurement ranges. These integrated projector-low RCS source support/sting pylons are particularly advantageous when deployed in a geometrically shaped measurement chamber, which chamber removes substantially all but direct path backscattered signals from the target of interest. A low RCS measurement system which exploits the novel integrated projector-low RCS source support/sting pylons is also disclosed.
A radar system tracks a target in response to an echo, i.e., a reflected portion of the incident radar signal, from the target of interest. Therefore, it is critical to the design and operation of radar systems to be able to quantify, or otherwise describe this echo, particularly in terms of target characteristics, e.g., size, shape and/or orientation. One such characteristic is radar cross-section (RCS), which is the projected area of a metal sphere returning the same echo signal as the target of interest, assuming the metal sphere is substituted for the target of interest. Unlike the echo signal from a sphere, which is orientation independent, the echo signal, and thus the RCS, varies as a function of orientation of the target of interest. This variation can be very rapid, especially when the target of interest is many wavelengths in size.
RCS values of simple bodies can be computed exactly by solution of a wave equation defined in a coordinate system for which a constant coordinate coincides with the surface of the body.
However, there is no known tactical target of interest which fits these solutions. The practical engineer cannot rely on predictions and calculations; the engineer must eventually measure the echo characteristics of the target of interest. This measurement can be performed on a full scale target of interest on an outdoor test range or on scale models to the target of interest in a measurement chamber. Current state of the art ranges include "compact ranges" which use a collimating reflector system to achieve the desired electromagnetic field distribution in the measurement zone (target area), i.e., to simulate a wide separation between the radar source and the target of interest.
Typical RCS chambers are rectangular rooms covered with Radar Absorber Materials (RAM). For a given target support system and antenna/radar system, the chamber performance is limited by the chamber size and shape and by absorber material employed. Cost limitations usually drive both the chamber size and the quantity and quality of the RAM installed in the chamber. The measurement capability in RCS chambers is limited by several factors, including:
(a) the chamber size and shape; PA1 (b) the type and amount of RAM applied to the chamber walls; PA1 (c) the target support system; and PA1 (d) the antenna/radar system. PA1 chamber means which surrounds a target of interest intersected by a line defined by focal points associated with the chamber means, for separating and extracting scattered signals scattered by the target of interest, the chamber means including a chamber having an interior defined by rotation of a nonlinear curve about the line, and first and second focusing elements which couple the scattered signals out of the chamber; PA1 a first structure for supporting the target of interest; and PA1 a second structure for generating signals scattered by the target of interest; PA1 wherein each of the first and second structures is coaxial with the line, and PA1 wherein each of the first and second structures is coincident with one of the focal points. PA1 a measurement chamber which surrounds a target of interest intersected by a line defined by focal points associated with the measurement chamber system and which separates and extracts scattered signals from the target of interest, the measurement chamber including at least one chamber having an interior defined by rotation of a nonlinear curve about the line, and first and second focusing elements which couple the scattered signals out of the chamber; PA1 a signal source which emits signals along the line, wherein the emitted signals interact with the measurement chamber to thereby produce the scattered signals; PA1 a source support pylon which supports the source and which couples the scattered signals out of the chamber; and PA1 a target support pylon, which supports the target of interest at one of the focal points, and which is coaxial with the line. PA1 a measurement chamber system which surrounds a target of interest intersected by a line defined by focal points associated with the measurement chamber and which separates and extracts scattered signals from the measurement chamber system, the measurement chamber system including a chamber having an interior defined by rotation of a nonlinear curve about the line, and first and second focusing elements which couple the scattered signals out of the chamber; PA1 a signal source which emits signals along the line, wherein the emitted signals interact with the target of interest to thereby produce the undesirable scattered signals and desirable backscattered signals; PA1 a source support pylon which supports an output element of the source and which couples the scattered signals out of the chamber; and PA1 a target support pylon, which supports the target of interest at one of the focal points, and which is coaxial with the line. PA1 a first end proximate to the source to which the target of interest is attached; PA1 a second end, which is disposed outside of the measurement chamber system, the second end further comprising means for adjusting the attitude of the target support pylon with respect to the line; PA1 a pivot element about which the target support pylon pivots; PA1 a cart supporting the target support pylon at the pivot element; and PA1 rails supporting the cart; PA1 wherein:
With respect to factors (a) and (b), the room, i.e., measurement chamber itself, construction is often the limiting factor in RCS measurement chambers. Radar reflections or echo signals are generated by scattering from the target of interest. Echo signals which are not direct paths, i.e., scattered signals, generally arrive at a later time than that the direct path backscattered signals and, thus, can contaminate the RCS measurement. The conventional method of "quieting" the radar reflections from the room itself is by treating the chamber walls with large pyramidal RAM up to six feet deep, which RAM attenuates the incident microwave energy.
With respect to factor (c), attempts have been made over the years to reduce the spurious scattered signals which contaminate RCS measurement, particularly those generated by the support for the target of interest, since the target support pylon is one of the main factors which limits the measurement capability of existing RCS measurement ranges. The three different kinds of support structures which are generally used in RCS measurement schemes are discussed immediately below.